A fuel tank of a motor vehicle is typically provided with a fuel vapor passage for expelling fuel vapor from the fuel tank and a fuel vapor canister provided in the fuel vapor passage for absorbing the fuel vapor. The fuel absorbed by the canister is drawn from the canister by the intake negative pressure of the intake system, and flows into the combustion chambers via the intake system. In this manner, the fuel vapor is prevented from being released to the atmosphere, and an excessive rise in the internal pressure of the fuel tank can be avoided.
In such a fuel tank, it is known to open out an end of the fuel vapor passage in an upper part of the fuel tank, and selectively close the open end with a float valve. The float valve moves up and down in dependence on the liquid level of the fuel tank so that the fuel vapor passage is closed when the liquid level rises beyond a prescribed value to prevent the fuel liquid from flowing into the fuel vapor passage. However, when a rapid rise in the liquid or bubbling of the fuel should occur, the fuel liquid could flow into the fuel vapor passage. To remove the fuel liquid that happens to flow into the fuel vapor passage, and prevent the fuel liquid from reaching the fuel vapor canister, it has been proposed to provide a gas liquid separation device in an intermediate point of the fuel passage. See Patent Document 1, for instance.
In the gas liquid separation device disclosed in Patent Document 1, the fuel liquid separated from the fuel vapor is expelled to the filler pipe that connects the filler opening with the fuel tank. The gas liquid separation device includes a main pipe that extends vertically and has a lower end extending into the filler pipe. The main pipe is closed at the upper end and opens out at the lower end. The interior of the main pipe is separated into a first passage and a second passage by a partition wall extending along the axial line of the main pipe. The upper end of the first passage is connected to the fuel tank side end of the fuel vapor passage, and the upper end of the second passage is connected to the canister side of the fuel vapor passage. The gas liquid separation device includes a normally open type flap valve device which is pivotally attached to the interior of the filler pipe to selectively close the lower end of the main pipe. The flap of the flap valve device is normally in the open position, and can be pushed into the closed position to close the open end of the main pipe by the filler nozzle inserted into the filler pipe during refueling. The flap is configured such that a gap is created between the flap and the partition wall when the flap closes the open end of the main pipe.
In this gas liquid separation device, the fuel vapor that flows through the fuel vapor passage is passed downward through the first passage, and upward through the second passage via the interior of the filler pipe before reaching the canister. The fuel liquid that may flow in the fuel vapor passage passes from the first passage to the filler pipe under the gravitational force, and does not reach the canister. During refueling, the open end of the main pipe is closed by the filler nozzle pushing the flap into the closed position so that the fuel liquid flowing through the filler pipe does not flow into the main pipe. When the open end of the main pipe is closed, the fuel vapor can pass through the gap between the partition wall and the flap, and flows into the canister via the second passage. On the other hand, the fuel liquid is trapped in the lower end of the main pipe or on top of the flap. When the filler nozzle is pulled out of the filler opening, and the flap opens as a result, the fuel liquid that may have collected on the flap flows into the filler pipe.